Light flavor-singlet scalars and walking signals in $N_f=8$ QCD on the lattice

Journal Article · Tue Jul 18 00:00:00 EDT 2017 · Physical Review D

DOI:https://doi.org/10.1103/PhysRevD.96.014508· OSTI ID:1392260

Aoki, Yasumichi ^[1]; Aoyama, Tatsumi ^[2]; Bennett, Ed ^[3]; Kurachi, Masafumi ^[4]; Maskawa, Toshihide ^[2]; Miura, Kohtaroh ^[5]; Nagai, Kei-ichi ^[2]; Ohki, Hiroshi ^[6]; Rinaldi, Enrico ^[7]; Shibata, Akihiro ^[4]; Yamawaki, Koichi ^[2]; Yamazaki, Takeshi ^[8]

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1. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Brookhaven National Lab. (BNL), Upton, NY (United States)
2. Nagoya Univ. (Japan)
3. Swansea Univ. (United Kingdom)
4. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)
5. Aix-Marseille Univ., Marseille (France); Nagoya Univ. (Japan)
6. Brookhaven National Lab. (BNL), Upton, NY (United States)
7. Brookhaven National Lab. (BNL), Upton, NY (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
8. Univ. of Tsukuba (Japan)

Based on the highly improved staggered quark action, we perform in this paper lattice simulations of N_f = 8 QCD and confirm our previous observations, both of a flavor-singlet scalar meson (denoted as σ) as light as the pion and of various “walking signals” through the low-lying spectra, with higher statistics, smaller fermion masses m_f, and larger volumes. We measure M_π, F_π, M_ρ, M_a0, M_a1, M_b1, M_N, M_σ, F_σ, (φφ) (both directly and through the Gell-Mann-Oakes-Renner relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: Ratios of the quantities to M_π monotonically increase in the smaller m_f region towards the chiral limit similarly to N_f = 4 QCD, in sharp contrast to N_f = 12 QCD where the ratios become flattened. We perform fits to chiral perturbation theory, with the value of F_π found in the chiral limit extrapolation reduced dramatically to roughly 2/3 of the previous result, suggesting the theory is much closer to the conformal window. In fact, each quantity obeys the respective hyperscaling relation throughout a more extensive m_f region compared with earlier works. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, γ_m ≃ 1, with the notable exception of M_π with γ_m ≃ 0.6 as in the previous results, which reflects the above growing up of the ratios towards the chiral limit. This is a salient feature (walking signal) of N_f = 8, unlike either N_f = 4, which has no hyperscaling relation at all, or N_f = 12 QCD, which exhibits universal hyperscaling. The effective γ_m Ξ γ_m(m_f) of M_π defined for each m_f region has a tendency to grow towards unity near the chiral limit, in conformity with the Nambu-Goldstone boson nature, as opposed to the case of N_f = 12 QCD where it is almost constant. We further confirm the previous observation of the light σ with mass comparable to the pion in the studied m_f region. In a chiral limit extrapolation of the σ mass using the dilaton chiral perturbation theory and also using the simple linear fit, we find the value consistent with the 125 GeV Higgs boson within errors. Finally, our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension γ_m ≃ 1 and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in the N_f = 8 one-family model.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Nagoya Univ. (Japan); Aix-Marseille Univ., Marseille (France)
• Sponsoring Organization: USDOE; Japan Society for the Promotion of Science (JSPS); Ministry of Education, Culture, Sports, Science and Technology (MEXT) (Japan); National Agency for Research (ANR) (France)
• Contributing Organization: LatKMI Collaboration
• Grant/Contract Number: AC52-07NA27344; SC0012704; 22224003; 16K05320; 15K05049; 16H06002; 25800138; 25800139; 15K17644; 25105011; ANR-11-LABX-0060; ANR-11-IDEX-0001-02
• OSTI ID: 1392260
• Alternate ID(s): OSTI ID: 1371805
• Report Number(s): BNL-114309-2017-JA; R&D Project: PO-3
• Journal Information: Physical Review D, Vol. 96, Issue 1; ISSN 2470-0010
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

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dynamical symmetry breaking models
extensions of Higgs sector
extensions of gauge sector
lattice field theory
nonperturbative effects in field theory
lattice gauge theory
particles & fields